Layer half the filo in the base and sides of a buttered 24cm-diameter, 4cm-deep metal pie dish, allowing pastry to overhang. Spoon in spinach mixture, fold in filo edges and loosely place remaining filo on top to cover. Brush pie with melted butter, bake until cooked through (1-1½ hours; cover loosely with foil if it starts to brown too quickly). Cool in dish for 5 minutes, then turn out, slice, and serve warm with a simple olive and herb salad.